While migration is not in itself a risk factor for poor health, conditions surrounding the migration process for the vast part increase vulnerabilities to ill health and HIV. Migrant adolescents and youth with irregular status studied in urban areas and along transit routes in and around cities have been shown to face barriers in access-ing basic services, owaccess-ing to factors of higher fees compared to nationals, cultural and language barriers, low health literacy including knowledge of the health system, real or perceived hostility by health-care workers and host community members and the absence of caregivers for young people (IOM 2011b ). Migrants subjected to exclusion, alienation and anonymity and in particular migrants in an irregular situ-ation can be disproportionately vulnerable to contracting disease and developing mental health problems (IOM 2011b ). Those parts of the city with concentrations of migrants are often diffi cult to reach with health information and services, and HIV programmes, already overstretched with the burden of disease in host communities, are not structured to cater for the needs of ‘invisible’ populations such as refugees, asylum seekers and undocumented migrants (IOM 2011b ).
A wide body of literature shows that across all continents, migration is associated with riskier behaviour, including sexual risk behaviour (Baumer and South 2004 ; Brockerhoff and Biddlecom 1999 ; Greif and Dodoo 2011 ; Sambisa and Stokes 2006 ; IOM 2011a ). Sampson and Laub ( 1993 ) in the early 1990s found that migra-tion from rural to urban centres is often associated with the weakening of existing bonds, which can in turn lead to an increased likelihood of nontraditional behav-iours. Beck et al. ( 1991 ) found that social control factors, such as religious systems,
1 The broad classifi cations for migrancy are economic migrant, documented/regular migrant, irreg-ular/non-documented migrant, refugee and asylum seeker.
socioeconomic position and family ties, affect the strength of these bonds in diverse ways during and after migration, a situation still evidenced today. Despite this early fi nding, research has not arguably suffi ciently explored the matter of migration and social bonds including mobility to and from the slums of Nairobi. The disruption of social networks can lead to patterns of nonnormative behaviour and give way to feelings of isolation and dislocation among migrants, factors shown to be key in understanding humiliation and risky behaviour (South et al. 2005 ). Young migrants, in particular, tend to gain easier acceptance into peer groups with higher rates of deviance including violent crime (Haynie et al. 2006 ; South et al. 2005 ).
Brockerhoff and Biddlecom ( 1999 ) provided a framework for studying differ-ences in overall behaviour of migrants, based on three broad lines of analysis: pre-disposing individual characteristics, changes in individual attributes due to migration, notably separation from a spouse or partner and exposure to a new social environment, with different sexual norms, opportunities and constraints that hold an infl uence over sexual behaviour. These three perspectives have over the course of the past two decades helped explain fertility differences between migrants and non-migrants as well as further explained the selectivity of migration, life disruptions associated with mobility and migrants’ adaptation to social expectations in new places of residence.
Mberu and White ( 2011 ) review the ‘selectivity hypothesis’, which posits that migrants are not randomly selected, but migration is selective in regard to personal characteristics such as higher education, young age, unmarried status and desire for upward social mobility. Attributes of these migrants predispose their behaviour to be different from nonmigrants, particularly regarding risky sex. According to the authors, the disruption hypothesis in the period immediately following migration is associated with physiological stress due to moving, loss of social capital and separa-tion from signifi cant others. The ‘adaptasepara-tion hypothesis’ proposes that migrants adapt to the new economic, social and cultural environment at the places of destina-tion, often resulting in marked behaviour change (Mberu and White 2011 ). The very act of making this voluntary movement, which often takes place over distance and time and between different sociocultural environments, with uncertain outcomes helps defi ne migrants as inherent risk-takers (Mberu 2008 , citing Peterson 1958 ; Massey et al. 1994 ). Moreover, migrants from the outset may be predisposed towards heightened risk-taking behaviour, including engaging in risky sex (Mberu 2008 , citing Brockerhoff and Biddlecom 1999 ). Risk-taking patterns of voluntary and non-voluntary migrants to the urban slums and particularly regarding patterns of convergence and assimilation need further investigation, especially given that both forms of migrancy to urban centres are increasing, globally.
The global evidence refl ects these arguments. Residential change, from one known universe to another, is associated with increased premarital and extramarital sexual relationships (Halli et al. 2007 ; Mberu and White 2011 ). These behaviours are all strongly associated with transmission of HIV and sexually transmitted dis-ease (STD) (Lurie 2006 ). Research into urban contexts in sub-Saharan Africa has documented that poor sexual and reproductive outcomes are shaped by early sexual debut, a factor often associated with migration (Gage 1998 ; Gregson et al. 2005 ;
Harrison et al. 2005 ; Pettifor et al. 2004 ). Drawing on data from the 2008 Nigeria Demographic and Health Survey, one study examined the patterns of internal migra-tion and sexual initiamigra-tion among never-married Nigerian youth aged 15–24 and showed that migrants generally demonstrate stronger association than nonmigrants and urban to rural and rural to rural migrants in particular, with premarital sexual initiation (Mberu and White 2011 ). In their study of the migration experience and premarital sexual initiation in urban Kenya, Luke et al. ( 2012 ) found that young people, both male and female, who migrate, either alone or as a family unit, during early adolescence tend to engage more in sexual activity. Luke et al. ( 2012 ) also pointed to the link between changes in place of residence with multiple and concur-rent sexual partners, premarital and extramarital sexual relationships and inconsis-tent condom use. Migration into urban areas, as held, exposes individuals to new ideas, more permissive social norms and sexual networks. Luke et al. ( 2012 ) con-clude that migration during formative adolescence and early adult years often leads to early sexual debut and other unsafe sexual practices.
The literature shows that the situation of adolescent young women is complex.
Certain dimensions of migration offer a degree of protection against early sexual initiation based on the number of residential changes in the last 1–3 months (Mberu and White 2011 ). Another study looking at youth in urban Kenya found that young women who migrated in the past month were two times more likely to enter a second (concurrent) sexual partnership, compared with those who did not recently migrate (Xu et al. 2010 ). The interaction between migration and behaviour change is complex and context dependent (Smith 1999 ). The literature also demonstrates that in Africa migration very often takes place within family and community networks and is a valuable form of support in helping young people adjust to life in a new environment.
These ties affect the sexual behaviour of young migrants, especially adolescent young women. Adolescent young women often face additional restrictive norms than boys and greater parental and community control of their behaviour, which has offered a degree of protection against risky sex (Browing et al. 2005 ; Luke et al. 2011b ).
Age of migration is a critical factor in understanding vulnerability and resilience (Luke et al. 2012 ). It is posited that early adolescents will face greater adjustment diffi culties than they would at later ages, particularly when they are less resilient to change (Luke et al. 2012 ). Lacking cognitive maturity, as Dixon-Mueller ( 2008 ) shows, young adolescents, particularly boys, can be driven to engage in risk-taking and sensation-seeking behaviour, including sexual activity. Young women, how-ever, may be more vulnerable to disruptions caused by migration during early ado-lescence owing to emotional and physical changes associated primarily with puberty and residential change and effect a ‘downward assimilation’ to peer groups identi-fi ed with risky behaviour (Luke et al. 2012 ). The evidence suggests that young women who faced early disruption but do not experience subsequent moves is an important factor in determining vulnerability and risky sexual behaviour (Luke et al. 2012 ). However, despite the evident differences in developmental and social processes between adolescent boys and young women, there is a noted lack of research on gender and sexual activities in the context of migration and in particular intra-urban mobility.
Luke et al. ( 2012 ) discuss migration and assimilation which involves numerous processes that serve to shape young people’s sexual behaviour. The key to patterns of assimilation is socioeconomic integration into new locations, which in turn impacts health behaviours including mortality and nutritional status (Luke et al.
2012 , citing Akresh 2007 ; Venters and Gany 2011 ; Reed et al. 2012 ). A large body of evidence points to the fact that migrants’ health often deteriorates over time in the new location including increasingly engaging in unsafe sexual activities (Luke et al.
2012 ). Furthermore, adolescents and young adults experiencing a new normative environment can feel traumatised and isolated in their efforts to integrate into peer networks (Luke et al. 2012 ). The notion of family disruption through change of resi-dence especially for already traumatised young people may well add to the sense of loss and substantially challenges resilience at all levels (Hosegood et al. 2007 ; Madhavan 2004 ; Mberu 2008 ). Empirical research has so far not explored if those experiences that can lead to humiliation for the young migrant are signifi cantly dif-ferent from the mobile intra-slum resident. Short of pointing to the wide practice of transactional sex as a means of survival, measures available to each social group to signifi cantly ‘dignify’ their respective worlds remain unclear.
The evidence indicates that residential change and family disruption during ado-lescence and early adulthood can have an effect on long-term health and develop-mental behaviours (South et al. 2005 ). Finding themselves in an alien environment, young people, as part of their efforts to assimilate, may seek out peer groups that encourage early sexual activity (South et al. 2005 ). Earlier research from North America indicates that the number of residential moves impact young people’s sex-ual behaviour as with each move, the likelihood of premarital sex increased by a factor of 5 per cent among 15–19-year-olds, which is refl ected in the experience drawn from related fi ndings in Nairobi (Stacks 1994 ). One conclusion drawn from this research is that numerous residential moves create a sense of transiency that gives way to temporary casual relationships. Again, the literature still fails to explain the long-term impact on sexual choices for migrants’ once long-term residency has been established and notably in highly insecure environments.
Women migrants, in particular, can face heightened vulnerability to HIV. Reasons given are vulnerability to sexual abuse and violence, neglect for their reproductive health needs and marginalisation from education, employment, goods and services (Carballo et al. 1996 ). In a study of HIV transmission and acquisition risk among female migrants in Kenya, Camlin et al. ( 2014 ) found that gendered aspects of the migration process – the circumstances that trigger migration, livelihood strategies available to female migrants and social features of migration destinations – are often associated with high risks of contracting HIV. Migrations were often triggered within the household often due to changes in marital status and gender-based vio-lence (Camlin et al. 2014 ). The evidence also showed that female migrants are often forced to engage in sex work as a way of supplementing earnings from informal sector trading. Additional evidence from Kenya indicates that young female urban migrants in Kenya often turn to sex work to earn a living and generally lack access to reproductive health services and crucial information and support for HIV preven-tion and treatment (Ngugi et al. 2012 ; IOM 2011a ). Despite the fact that the Kenyan
national response is increasingly targeting research and programming towards key population groups, migrant female sex workers are not seen as a discreet group.
IOM ( 2011a ) reported that in one study carried out among migrant female sex workers in Nairobi, half (52.2 per cent) were between the ages of 20 and 29 and with an overall HIV prevalence of 23.1 per cent. The study also demonstrated low levels of education and literacy among migrant female sex workers, making it harder to fi nd work in the formal employment sector; and whereas nearly all respon-dents had heard of HIV, knowledge around prevention and transmission was mixed and demonstrated with many misconceptions (IOM 2011a ). The report concluded that migrant female sex workers are marginalised by social determinants of health, in particular, irregular migration status, lack of fl uency in local languages and cul-tural barriers (IOM 2011a ).